Cooperative Research

Fertilizer Rate Affects Marketable Yield of Cos Lettuce in Nutrient Film Technique (NFT) Hydroponic System

 Principal Investigator: Dr. Jonathan Egilla
Tel: (573) 681-5621

Most plants species commonly grown in Nutrient Film Technique (NFT) hydroponic system will tolerate a wide range of nutrient concentrations. Mason (1990) reported trials in which no significant losses in yield resulted from varying nitrogen (N) concentration between 10 and 320 mg/liter. Stoughton (1969) recommended that nutrient solution for general use in NFT hydroponic systems should contain 100 to 300 mg N/liter. Currently the total N in most hydroponic solution formulas range from 100 to 200 mg/liter (Jones, 2005). Inadequate supply of N can cause reduction in plant growth, quality and final yield, especially if it occurs during critical stages of plant growth. Plants supplied with excess N produces lush growth with dark green foliage, have greater sensitivity to changes in environmental conditions, and are susceptible to disease and insect attack. The marketable yield for  lettuce (Lactuca sativa L. var. longifolia Lam.) ‘Cimmaron.’was evaluated at two concentrations of Peters Peat-Lite Special® solution in NFT system. The two fertilizer treatments consisted of 1) optimum N (200 mg N/liter), and 2) low N (100 mg N/liter). While the pH of the recirculating nutrient solution for both treatments was maintained at about 6.0, mean electrical conductivity (EC) was 2.29 mS/cm at optimum N compared with 1.23 mS/cm at low N. Average day/night ambient temperature was 39.1 oC and 32.8 oC, with a mean of 30.5 oC, and day/night relative humidity (RH) was 81.3 % and 55.0 %, respectively. Two-week old lettuce seedlings transferred into NFT troughs at the first true-leaf stage were harvested 30 days later. Marketable yield (mean fresh weight [g/head of lettuce]) decreased by 30.5 % at low N compared with optimum N, consistent with 43.5 % and 17.5 % decrease in dry weight and dry weight ratio (dry weight/fresh weight), respectively.
These findings improve grower knowledge about hydroponic nutrient solution composition and use, which represent the greatest challenge to all hydroponic/soilless growers. A soundly based understanding of nutrient solution management, on which literature information is most limited, is as important to successful hydroponic culture as the lists of nutrient formulas, preferred reagent sources and the weights and measures often published in textbooks. Better plant nutrient management through the supply of optimum rather than excess or suboptimum levels in NFT systems can improve profitability through 1) increased lettuce yield and quality 2) reduction of plant nutrient costs, and 3) reduction in losses by enhancing root nutrient uptake, which can also minimize environmental pollution.
Literature Cited
Jones, B.J.               Hydroponics: A Practical guide for the soilless grower. Second edition.
                             CRC Press, New York, USA. pp. 38-41. 2005. 
Mason, J.                Commercial hydroponics: How to grow 86 different plants in hydroponics.
                             Kangaroo Press, Sydney, Australia. pp. 36-43. 1990.
Stoughton, R.H.        Soilless cultivation and its application to commercial hydroponic crop production.
                             United Nations Food and Agriculture Organization. Rome. 1969.